1. Field of the Invention
The present invention relates to an imaging apparatus comprising an imaging lens, and an image pickup device which is placed behind the imaging lens, and also to a portable apparatus comprising the imaging apparatus.
2. Description of the Related Art
In many recent portable telephones, an imaging apparatus is mounted. A portable telephone itself has a small and thin structure. In the case where an imaging apparatus is mounted in a portable telephone, therefore, the imaging apparatus to be mounted in the portable telephone is requested to have a structure which is smaller and thinner than the small and thin structure of the portable telephone.
In some of such imaging apparatuses which are requested to have a small and thin structure, a voice coil motor is used in order to simplify the structure of a portion for holding an imaging lens, and that of a lens drive portion which moves the imaging lens in the optical axis direction (for example, see Japanese Utility Model Registration No. 3,120,599 and JP-A-2005-50519).
FIG. 1 is a view showing an example of the configuration of an imaging apparatus comprising a voice coil motor.
The imaging apparatus shown in FIG. 1 comprises: a lens module 100 having an imaging lens 10, and a voice coil motor (hereinafter, referred to as VCM) for driving the imaging lens 10; an image pickup device 103 which is placed behind the imaging lens provided in the lens module 100; an imaging circuit 12 which produces a signal indicative of the driving direction and position of the imaging lens based on an image signal produced by the image pickup device 103; and a VCM driving circuit 13 which drives the VCM provided in the lens module 100 in accordance with the signal from the imaging circuit 12 indicating the driving direction and the driving position. Actually, the lens module 100 and image pickup device 103 which are shown in FIG. 1 are integrally configured. In the following description, therefore, they are generically referred to the imaging unit 10.
FIG. 2 is a view illustrating the internal configuration of the imaging unit 10.
FIG. 2A shows the internal configuration of the imaging unit 10, and FIG. 2B shows the state where coils 102a, 102b provided respectively in VCMs in the imaging unit 10 are energized by the VCM driving circuit 13 shown in FIG. 1, and an imaging lens 1000 is moved together with the coils 102a, 102b, by broken lines.
FIGS. 2A and 2B show the configuration where two magnets 101a, 101b provided in the imaging unit 10 shown in FIG. 1, and the two coils 102a, 102b which are placed in magnetic fields formed by the magnets 101a, 101b, and which, upon an input of a current, receives a force in the optical axis direction to move the imaging lens 1000 to a position corresponding to the current signal are disposed on the both sides of the imaging lens 1000. Actually, boards are fixed to a holding portion which holds the lens, and windings serving as the coils are formed on the boards, respectively.
The configuration will be described with reference to FIGS. 2A and 2B.
As shown in FIGS. 2A and 2B, the image pickup device 103 is fixed to the middle of a board 110 which is larger than the external shape of the image pickup device 103, and springs SP1, SP2 are disposed on the board 110 on the both sides across the image pickup device 103, respectively. The two coils 102a, 102b are extensibly supported by the springs SP1, SP2, respectively, and the imaging lens 1000 is held from the both sides by the coils 102a, 102b. The magnets 101a, 101b are disposed outside the coils 102a, 102b. The N- and S-poles of the magnets 101a, 101b are juxtaposed. The coils 102a, 102b which are placed in the magnetic fields formed by the magnets 101a, 101b are vertically disposed across the imaging lens 1000 of FIG. 2. The two coils 102a, 102b and the two magnets 101a, 101b cooperate to move the imaging lens 1000 against the spring urging or in the direction of the spring urging.
Namely, when a current is supplied from the external VCM driving circuit 13 to both the one coil 102a and other coil 102b which are provided in the two VCMs, a magnetic fields is generated in each of the coils 102a, 102b existing in the magnetic fields formed by the both magnets 101a, 101b, an interaction between the magnet 101a and the coil 102a causes the imaging lens 1000 to be moved together with the coil 102a, and that between the magnet 101b and the coil 102b causes the imaging lens 1000 to be moved in the optical axis direction together with the coil 102b. 
FIG. 3 is a view showing a current supplied to the coil 102, and a displacement of the imaging unit 10 incorporating the imaging lens.
FIG. 3A shows an input waveform of the current supplied to the coils 102a, 102b when the imaging unit 10 is to be moved from a position before movement to that after movement. FIG. 3B shows a displacement of the imaging lens 1000 which, when a current is caused to flow through the coils 102a, 102b by the input waveform, receives a force due to interactions between the currents flowing through the coils 102a, 102b and the magnets 101a, 101b, to be moved in the optical axis direction. The ordinate in FIG. 3A indicates a driving current, and the abscissa indicates the time (second). The ordinate in FIG. 3B indicates the displacement of the imaging lens, and the abscissa indicates the time (second).
When a current of 80 mA is supplied to each of the coils 102a, 102b in a step-like manner as shown FIG. 3A, for example, the imaging lens 1000 is moved to a position in the vicinity of 0.45 mm from the position before movement, and is stopped there.
In the structure shown in FIG. 2, however, the coils 102a, 102b are supported by the springs SP1, SP2 so as to be extensible in the optical axis direction, and therefore, when a step-like signal is supplied to the coils 102a, 102b and the coils 102a, 102b are vigorously moved together with the imaging lens 1000, a large external force is suddenly applied to the springs SP1, SP2 supporting the coils 102a, 102b. As a result, the springs SP1, SP2 vibrate, and, in the case of the example shown in FIG. 3B, the imaging unit is slowly stopped after an elapse of 0.2 seconds.
In the case where a mobile unit such as an imaging lens is disposed in a small and thin structure of a portable telephone or the like, it is often that, in order to movably hold an imaging lens as shown in FIG. 2, the imaging lens or the like is held by using an elastic spring or the like.